The present invention relates to a method and apparatus for severing packaging material, and more particularly, for severing packaging material which extends between successive wrapped loads during a continuous wrapping process.
Stretch wrapping is a method of wrapping loads with a tensioned web of packaging material such as stretch wrap film. An example of a method and apparatus for stretch wrapping is disclosed in U.S. Pat. No. 4,317,322 to Lancaster et al., assigned to Lantech, Inc., and is incorporated herein by reference.
Recently, developments in stretch wrapping have focused on methods and apparatus for continuously wrapping a series of loads in an uninterrupted manner. Such continuous wrapping involves conveying a series of loads through a wrapping area in which the loads are spirally wrapped with stretch wrap film. As a result, the series of loads become encased with a continuous tube of stretch wrap film. A severing bar, positioned downstream of the wrapping station, is passed between successive wrapped loads. The severing bar severs the tube of plastic material between successive wrapped loads and separates the wrapped loads.
As it has become possible to wrap at higher speeds, the conveying speed of the wrapped loads has also increased. To prevent the severing bar from striking the rapidly moving loads, it has become necessary to translate the severing bar in the conveying direction along with the loads while passing it between successive wrapped loads.
To reliably sever the packaging material on a prolonged and repeated basis, a heating element is incorporated in the severing bar to heat the severing bar so that the packaging material is melted or substantially weakened upon coming in contact with the severing bar. The heating element in the severing bar is supplied with electricity by an electrical conductor which is connected to a power source.
The complexity of the severing mechanism has substantially increased along with the need for high precision and the possibility of malfunctions. With such mechanisms, a malfunction could easily damage the severing mechanism, cause extensive delays during downtime for repairs, and cause fires if a heated severing element remains in prolonged contact with a load which is being wrapped.
An example of a method and apparatus for severing packaging material between successive wrapped loads during a continuous wrapping process is disclosed in U.S. Pat. No. 4,738,079 to Lancaster et al., assigned to Lantech, Inc., which is incorporated herein by reference. In the arrangement disclosed in the drawing of that patent, the load is transported along an even horizontal path by a series of conveyor belts. In the area of the severing mechanism, the conveyor belt follows a V shaped path below the horizontal load path to allow the severing bar to pass below the load path to ensure having the severing bar cut through the entire film tube including the lower portion of the film tube.
This design and other designs creating a gap in the conveyor bed were found to have drawbacks. For example, it was not completely satisfactory when used with a severing element which moved in a pattern which included movement in the conveying direction during cutting. It also was not completely satisfactory in avoiding and resolving jams which occurred when the severing element was unexpectedly and undesirably contacted by the load.
Using a flat conveyor belt surface at the severing station also was not completely satisfactory because there were times when the severing element would not cut the bottom of the film tube.
Accordingly, it is an object of the present invention to provide a method and apparatus for severing packaging material in which the severing element reliably cuts through the complete film tube and which does not jam or prevent the series of wrapped loads to be reliably conveyed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.